(1) Field of the Invention:
This invention relates to a process for producing halobenzophenone derivatives useful as monomers for heat-resistant polymers.
(2) Description of the Related Arts:
In recent years, halobenzophenone derivatives have attracted particular attentions as monomers for heat-resistant polymers such as polyether ketones and polythioether ketones. There is hence an outstanding demand for the development of a process permitting their production at a lower cost. Regarding production processes for halobenzophenone derivatives, for example, 4,4'-dichlorobenzophenone, it has been well known to obtain it by oxidation of 1,1-dichloro-2,2-bis(4-chlorophenyl)ethylene. As such processes, oxidation with chromic acid has been reported, for example, by J. Forrest, et al. in J. Chem. Soc., 333 (1946) and by H. L. Bradlow, et al. in J. Amer. Chem. Soc., 69, 662 (1947). In addition, oxidation of 1,1-dichloro-2,2-bis(4-chlorophenyl)ethylene with nitric acid in an organic solvent has been reported by O. G. Backeberg and J. L. C. Marais in J. Chem. Soc., 803 (1945); in Japanese patent application Laid-Open No. 26829/1983, etc. As another organic solvent, acetic acid is used in the former publication while a halogenated aliphatic hydrocarbon is employed in the latter publication.
The above-described conventional processes for the production of halobenzophenone derivatives are, however, accompanied by various problems. Namely, the process relying upon the oxidation with chromic acid consumes a large amount of chromic acid in the reaction. Further, it is necessary to cope with environmental problems including waste water disposal. This process therefore requires a significant cost so that it is difficult to industrially practice it under the circumstances.
On the other hand, the processes including the oxidation with nitric acid require the use of an organic solvent and therefore, substantial energy is needed for the recovery of the organic solvent. Besides, these processes still involve some unsolved environmental problems. For example, the use of a halogenated aliphatic hydrocarbon as solvent is accompanied by a problem, because there is a concern of deleterious influence to the environment so that more stringent limitations will certainly be imposed on its use in the future.
Regarding the processes relying upon oxidation with nitric acid, development of a new process is described as a substitute for the processes using an organic solvent, such as the processes as described above, from the viewpoints of economy and also environmental problems. From such viewpoints, one may consider directly oxidizing 1,1-dichloro-2,2-bis(4-chlorophenyl)ethylene with nitric acid for the production of 4,4'-dichlorobenzophenone without using any organic solvent. It has, however, been known that the nitric acid oxidation without an organic solvent results in the formation of nitrated substances, whereby the yield of 4,4'-dichlorobenzophenone as the target product is lowered (See O. G. Backeberg and J. L. C. Marais: J. Chem. Soc., 803 (1945)).
As has been described above, the use of an organic solvent is essential for the oxidation of 1,1-dichloro-2,2-bis(4-chlorophenyl)ethylene with nitric acid under the present circumstances. Thus, problems still remain unsolved from the viewpoints of economy and environmental problems.